In many integrated circuits applications, both AC and DC signals are converted to digital form using dedicated analog-to-digital converters (ADC)—i.e., one ADC for AC signals, and another ADC for DC signals. The use of dedicated ADCs is necessitated by the very different nature of the signals themselves. AC signals such as audio signals or RF signals vary significantly over a short period of time, but are generally contained within a specified frequency range. In such applications, the required performance of the ADC relates to signal-to-noise ratio, dynamic range, and the like, while offset and gain errors are tolerable. Over-sampled sigma-delta noise shaping ADCs are often used in this type of application.
DC signals, in contrast, do not vary significantly over a short period of time, and include such signals as battery voltage, charging current, digital-to-analog converter (DAC) output voltage under calibration, and the like. In such applications, where low offset and gain error are desired, low speed Nyquist rate ADCs (SAR, dual slope, etc.) or over-sampled incremental ADCs are often used. Incremental ADCs provide precision DC measurement (i.e., greater than 16 bit), but the standard sigma-delta noise-shaping ADC can not be directly used as an incremental ADC.
Accordingly, it is desirable to provide an ADC circuit that can be used for processing both AC and DC signals. Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.